The HER-2/neu proto-oncogene is over-expressed in about one fourth of the mammary carcinomas. HER-2/neu protein over-expression is frequently associated with human pathologies including multiple cancers; cancers of the pancreas, stomach, cervix, endometrium, fallopian tube and ovary are often the result of deregulated HER-2/neu HER-2/neu-mediated pathology is clinically correlated with poor prognosis, poor response to endocrine- and chemotherapies and the patients often have earlier relapse and shorter over all survival. The HER-2/neu gene is both amplified and actively transcribed from its promoter. Transcription factor AP-2, which is concomitantly deregulated in these mammary carcinomas, has been identified as a critical factor that activates HER-2/neu gene and causes its over-expression. We have shown earlier that over-expression of AP-2 induced tumorigenicity in a human teratocarcinoma cell line PA-1. Analysis of the AP-2 mediated tumorigenicity revealed that the activity of AP-2 could be controlled by its co-activators. We found two co-activators of AP-2; PC4 and poly ADP-ribose polymerase. Further, we demonstrated that these co-activators could be used as a tool to suppress the tumorigenicity of PA-1 cell line effective. In this proposal, I will investigate the mechanism of deregulation of AP-2 and HER-2/neu genes. First, the important regulatory sequences including the elements involved in mammary carcinoma-specific expression will be identified in the 5' flanking DNA sequences of AP-2 genes. Negative and positive regulatory sequences will be evaluated in various mammary carcinoma cell lines. Methodologies to interfere with the activation of AP-2 gene promoter and reduce the level of AP-2 gene promoter and reduce the level of AP-2 protein will be explored. Second, the inhibition of the HER-2/neu gene promoter activity will be studied using expression vectors that encode mutated AP-2 molecules such as truncated AP-2 with its DNA-binding domain or dimerization domain or anti-sense AP-2 mRNA molecules. Co-activators of AP-2, PC4 and poly ADP-ribose polymerase, have tremendous potential to alter the level of AP-2 activity. The effect of these molecules on HER-2/neu gene will be determined. Stable mammary cell lines expressing these proteins will be established and tested for their tumorigenic potential such as colony formation on soft-agar and induction of tumors in nude mice. Effective molecular therapeutical methods for suppression of HER-2/neu mediated human cancer will be derived from these investigations. The studies will generate potential markers to diagnose breast cancer and other human cancers using AP-2, its co- activators, the regulatory factors of AP-2, and HER-2/neu genes.